Armature



Oct. 7, 1969 c, PRATT ET AL 3,471,731

ARMATURE Filed June 13. 1967 9/ INVENTORS 7 l0 ROBERT M. PIERCE eLEONARD a. PRATT AGENT United States Patent US. Cl. 310-234 11 ClaimsABSTRACT or THE DISCLOSURE A durable armature structure which providescushioning under the commutator leads to prevent breakage thereof, andhas a fiber glass insulator between the commutator and the shaft.

This invention relates to armatures for electro-dynamic machines, andespecially to an improved, durable armature structure.

It is conventional in prior art to fix the commutator leads, to preventtheir-breakage, by means of a heavy coating of varnish or plasticmaterial. This has been necessary due to the vibrations and oscillationsto which the leads are subjected when the armature is rotated in theelectrod-ynamic machine. Unless the leads are somehow protected againstor made to accommodate for these stresses they exhibit fatigue and thenbreakage results. Some practices known in the prior art have acushioning arrangement underneath or overlying the leads, or a portionthereof, adjacent the commutator. Commonly, the leads are prepared inlengths providing for, firstly, a slack portion. Then'theslack portionis taken up in a binding-of resilient material or rio-to draw theresidual unbound portion of the leads taut. The binding put about theleads, or cushioning placed'underneath and having binding holding theleads thereto, is disposed with a lead-receiving surface c'o-axial withthe shaft. Yet, customarily, the leads radiate fromthewindings' inangular fashion. That is, they diverge from the. windings innerdimension outward to the bars, or converge from the windings outerdimension to the bars. With rotation of the armature, the forces ofvibration and oscillationto which the leads are subjected proceed fromthe angular plane in which the leads lay. Where the binding is co-axialwith the shaft, rather than co-angular with the leads, a torsionaleffect acts upon the leads at the terminus of the binding. Some otherknown practices use a heavy coating of varnish or plastic material tocreate a rigid mass over and about the leads at the commutator. Thedifiiculty with these arrangements arises from the rigidity they attemptto create. There is always a small degree of relative movement betweenthe commutator and the windings, due to impact loading of the machine.Thus, where the leads are so rigidly fixed that they cannot exhibit somegive, some will eventually snap at either ends of the rigid massimmediately adjacent the windings or the commutator.

Further, in prior art, it is conventional to form the commutator hub ofmolding material having a given dielectric value to insulate thecommutator bars from the shaft. However, under conditions of elevatedtemperature it is known that the molding material will exhibit adielectric breakdown and allow current leakage. Asbestos-filledphenolics, commonly used, carbonize at high temperatures, providing anelectrically-conductive material thereby. Further, the molding materialis quite frangible and subject to breakage or fracturing upon assemblyof the hub to the shaft. Especially is this so, when the shaft isknurled to receive the hub and to hold it fast. As a result,manufacturers try to achieve close tolerances of the internal diameterof the hub and the outside diameter of the shaft to avoid rupture of thehub while assuring a firm fit of same on the shaft. This is difiicult toachieve, and results in the scrapping of many damaged andout-oftolerance hubs. Accordingly, it is an object of the presentinvention to provide an improved armature structure with cushioningmeans for the leads which lay in angular disposition, whereby the leadsare free to have a controlled give, a damped flexure, across theirangular disposition. It is another object of this invention to overcomethe priorly-cited difiiculties by providing an armature structure havingan enhanced dielectric strength and which requires less exactingmanufacturing tolerances.

A feature of this invention comprises the use of ahighdielectric-strength, fiber glass sleeve between the commutator andthe shaft. Another feature of this invention is in the use ofespecially-shaped washers, annuluses of given configuration, on theshaft against which the commutator leads lay restrained, in dampedflexure, in their angular disposition.

Further objects and features of this invention will become more apparentb reference to the following description taken in conjunction with thefigures in which:

FIGURE 1 is a side view in elevation of an armature according to theinvention;

FIGURE 2 is a side view, partially in cross-section of the armature ofFIGURE 1; and

FIGURE 3 is a side view, partially in cross-section of anotherembodiment of the invention.

As shown in FIGURE 1 the armature, according to the invention, has ashaft 1 with windings 2 and a commutator structure 3 mounted thereon inspaced relationship. Commutator leads 4 are arranged between the windingand the commutator structure at an angle, and lie over an annulus 5disposed on the shaft 1 between the commutator structure 3 and thewindings 2. The annulus 5 is a cone-shaped washer of resilient andelectrically-insulating material, for example: rubber. The angle of thecone shape of the annulus 5 corresponds to the angle defined by thecommutator leads 4 in their interconnection between the windings 2 andcommutator structure 3. Yet, the size of the annulus in cross-section,with respect to the annular space bounded by the array of commutatorleads 4 and the shaft 1, is greater. This insures a light restraint ofthe leads and a nesting of each, along the fully exposed length thereof,in resulting depressions formed in the annulus. Cording 6 is wound aboutthe leads 4 to insure the nesting of them on the annulus 5. FIGURE 2shows the inventive arrangement in more detail, and illustrates thecommutator structure which includes the core 7, which may be of an epoxyresin or similar molding material, with commutator bars 8 arrangedthereabout. Fiber glass sleeve 9 is interposed between the shaft 1 andthe core 7, providing for electrical insulation and improved dielectricstrength of the commutator structure. In teaching the use of a fiberglass sleeve 9, this invention avoids the severe manufacturing tolerancerequirements necessitated prior thereto. As fiber glass has a measurabledegree of compressibility, and whereas the commutator core 7 hasvirtually none, assembly of the core 7 to the shaft 1 is greatlysimplified. The stresses and abrading which are incident in assembly areaccepted by the fiber glass sleeve 9 without damage thereto, and thediameters concerned with the shaft 1 and core 7 interface need be lesscritical. Further, the fiber glass sleeve 9 provides a more certainbonding between the core 7 and the shaft 1. The conventional corematerials, like the metallic shaft itself, have a low coefiicient offriction, hence the practice of knurling the shaft. The fiber glasssleeve 9, however, militates against any possible slippage between thecore 7 and the shaft 1. The customary stresses, to which the fiber glasssleeve 9 is subjected at assemblyand in dynamic use in the machine-leaveits dielectric strength unaltered and its physical dimensions andconfiguration virtually'unchanged. Index numeral 10 denotes the nestingof leads 4 into the annulus 5. According to a preferred embodiment ofthe invention, the fiber glass sleeve 9 is molded into the commutatorstructure 3, and the annulus 5 is assembled on the shaft 1, before theleads 4 are connected to the commutator bars. Other embodiments of theinvention will occur to those skilled in the art. For instance, it maybe found advantageous, in some applications, to mold the fiber glasssleeve 9 to the shaft 1, without departing from the spirit of ourinvention. Shaft insulation 11 is disposed betweenthe windings 2 and theshaft 1. I

In FIGURE 3, is shown another embodiment of our invention wherein theannulus 12 is formed of twin cones to receive the leads. The cording 6is wrapped around the leads to nest them in the center of thetwin'cones, leaving them free to manifest a give, a damped flexure, withthe vibrations of the machine.

While ,we have described above the principles of our invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of our invention as set forth in the objects thereof and inthe accompanying claims.

We claim:

1. An armature comprising:

a shaft;

a commutator structure and a plurality of windings mounted on said shaftsaid structure andsaid plurality having a space therebetween; saidcommutator structure comprising a hub of material of given dielectricvalue having electricallyconductive bars radially arranged thereon; anarray of leads connecting, and disposed between, said windings and saidbars each of which leads lay in wholly angular disposition, with respectto the axis of said shaft, along the full length of said leads whichtraverse an annular area bounded by said array, and which area extendsfrom said windings tosaid bars; a resilient first member, having aconfiguration which exactly corresponds with the configuration of saidarea, and in contact with said leads to cushion said leads;

said first member being effective to maintain said leads in said angulardisposition; and a second member, having a dielectric value greater a 4I than said given value, interposed between said commutator structureand said shaft.

2. The invention, according to claim 1, further comprising: meansoverlying said leads to restrain them on said first member.

3. The invention, according to claim 1, wherein: said resilient firstmember is in contact with said-leads along the full lengths thereof. 1

4. The invention, according to claim 1, wherein said second member isformed of compressible material which exhibits superior hoop and tensilestrength.

. 5. Theinvention, accordingio claim 1, wherein said second member isformedof fiber glass.

6. The invention, according to claim 1, wherein said second membercomprises a sleeve of dielectric material fixed to the inside diameterof said commutator structure.

7. The invention, according to claim 1, wherein-said second membercomprises a sleeve of dielectric material molded into said commutatorstructure.

8. The invention, according to claim 1, wherein said resilient firstmember comprises an annulus having a circular cross-section.

, 9. The invention, according to claim 1, wherein said I resilient firstmember comprises an annulus having a triangular cross-section.

g 10. The invention, according to claim 1, wherein said resilient firstmember comprises an annulus having a plurality of triangularcross-sections. 1

11. The invention, according to claim 1, wherein said resilient firstmember is formed of electrically-insulating material. I 1 q ReferencesCited 'UNITED STATES PATENTS 45 MILTON o. HIRSHFIELD, Primary ExaminerMARK O. BUDD, Assistant Examiner US. .Cl. X.R. 310-235, 270 g

